From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH] fix bad behavior in use_hierarchy file Date: Tue, 26 Jun 2012 02:26:48 +0400 Message-ID: <4FE8E5A8.6020106@parallels.com> References: <1340616061-1955-1-git-send-email-glommer@parallels.com> <20120625204908.GL3869@google.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120625204908.GL3869-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Tejun Heo Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Andrew Morton , devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Dhaval Giani , Michal Hocko , Kamezawa Hiroyuki , Johannes Weiner On 06/26/2012 12:49 AM, Tejun Heo wrote: > On Mon, Jun 25, 2012 at 01:21:01PM +0400, Glauber Costa wrote: >> I have an application that does the following: >> >> * copy the state of all controllers attached to a hierarchy >> * replicate it as a child of the current level. >> >> I would expect writes to the files to mostly succeed, since they >> are inheriting sane values from parents. >> >> But that is not the case for use_hierarchy. If it is set to 0, we >> succeed ok. If we're set to 1, the value of the file is automatically >> set to 1 in the children, but if userspace tries to write the >> very same 1, it will fail. That same situation happens if we >> set use_hierarchy, create a child, and then try to write 1 again. >> >> Now, there is no reason whatsoever for failing to write a value >> that is already there. It doesn't even match the comments, that >> states: >> >> /* If parent's use_hierarchy is set, we can't make any modifications >> * in the child subtrees... >> >> since we are not changing anything. >> >> The following patch tests the new value against the one we're storing, >> and automatically return 0 if we're not proposing a change. > > A bit of delta but is there any chance we can either deprecate > .use_hierarhcy or at least make it global toggle instead of subtree > thing? This seems needlessly complicated. :( > I am for deprecating. If this is a long term goal, a two-phase process making it per-tree seems unnecessary and even more confusing.